1. Field of the Invention
The present invention relates to marine exhaust systems and more particularly to a marine exhaust system for discharging marine engine exhaust below the surface of the water.
2. Description of the Prior Art
Marine exhaust systems found on motorized vessels typically discharge engine exhaust through discharge ports located above the water line towards the rear of the vessel or stern. Marine engine exhaust comprises a mixture of gas and cooling water. Conventional marine exhaust systems, typically known as water lift mufflers include: an internal combustion engine having at least one exhaust manifold for ducting engine exhaust to a muffler wherein exhaust gas sound is attenuated, and an exhaust pipe originating at the muffler and terminating at a discharge opening in the hull, located proximate the stern. Engine exhaust is discharged toward the rear of the vessel and above the water line where, in theory, the gases are dissipated or carried away from the vessel.
There are a number of inherent disadvantages present in the conventional prior art marine exhaust systems and methods. Firstly, Engine exhaust must first pass through a muffler so that excessive noise may be attenuated prior to discharge. Since marine exhaust includes a corrosive mixture of gas and water, marine mufflers must be rugged and are known to add substantial cost and weight to vessels. Secondly, when a vessel is at idle, engine exhaust gas tends accumulate around the vessel since the discharge ports are sized for higher exhaust flow rates, and low flow exhaust flow rates, like those experienced at idle or low speed, are not discharged with sufficient velocity to completely clear the area. Thus, engine exhaust discharged through hull openings may accumulate in proximity to the vessel thereby irritating those on board, unless carried away or dissipated by prevailing winds. Thirdly, most motorized vessels that incorporate conventional marine exhaust systems suffer from a problem resulting from the low pressure area formed behind a moving vessel, often referred to as the "station wagon effect". Typically, a low pressure area, caused by the vessel structure moving through the atmosphere, develops near the stern of a vessel. Engine exhaust discharged near the stern of a moving vessel therefore, is caught in the resulting low pressure area and recirculates into the passenger compartment thereby irritating those on board. Since engine exhaust includes carbon monoxide gas, a high exhaust gas concentration circulating within the passenger compartment is extremely undesirable.
The prior art reveals a number of attempts directed toward overcoming the aforementioned problems. For example, U.S. Pat. No. 5,234,364 issued to Ito, discloses an EXHAUST SYSTEM FOR SMALL PLANING BOAT. Ito teaches an exhaust system having an exhaust pipe which terminates in a flush discharge opening formed in a lower surface of the hull for discharging engine exhaust through the body of water in which the watercraft is operating. The system incorporates an expansion chamber for silencing engine exhaust, and a low speed exhaust discharge line extending from the highest portion of the exhaust pipe, through the hull, to an area above the water level so as to provide a low speed exhaust discharge for discharging exhaust when the watercraft is operating at idle or low speeds. Discharging engine exhaust through a flush hull opening below the surface, however, causes the exhaust to flow with the fluid boundary layer formed by the water on the moving hull and results in the exhaust surfacing immediately behind the craft where the exhaust is likely to recirculate within the passenger compartment because of the aforementioned station wagon effect.
U.S. Pat. No. 5,078,631 issued to Harbert, also discloses a MARINE EXHAUST SYSTEM. Harbert discloses a marine exhaust system for separating the gas from the water of a gas/water mixture produced by a marine engine and expelling the gas a sufficient distance from the hull of a boat to place it outside of the turbulent boundary layer surrounding the hull and the low pressure area following behind the boat. Harbert, however, relies on an intricate variable exhaust gas discharge outlet that reduces the outlet opening area at low flow rates for projecting exhaust gases a maximum distance from a boat hull, and does not contemplate discharging exhaust gases below the surface of the water.
U.S. Pat. No. 4,509,927, issued to Ikeda, discloses a BOTTOM EXHAUST HIGH SPEED BOAT having a hull including a grooved bottom. Ikeda teaches an engine exhaust pipe extending into a midportion of the grooved bottom, and a duct fixed to the surface of the hull extending between the opening of the exhaust pipe and the front of the grooved bottom for transporting exhaust gases to the front of the grooved bottom whereby the grooved bottom is filled with exhaust gases thereby decreasing frictional resistance.
As has been described, the prior art has not overcome the aforementioned problems with marine engine exhaust. Thus, there still exists a need for a marine engine exhaust system for muffling a marine engine and discharging engine exhaust a sufficient distance from an idling vessel such that exhaust gas does not concentrate in proximity to the passenger compartment, and that discharges exhaust below the surface of the water, beyond the fluid boundary layer formed on the bottom of the hull while cruising, such that the discharged exhaust is further muffled and surfaces behind the low pressure area following the vessel thereby preventing recirculation within the passenger compartment.